My MCP Server Has 8 Tools and Zero Log Lines. Diagnosing a Failure Meant Guessing From the Outside.

Back in July my scheduled DEV.to publishing run failed at the very first step — the quota check couldn't reach dev.to:443 at all. Diagnosing it took manually running curl $HTTPS_PROXY/__agentproxy/status from inside the session and reading a proxy diagnostic by hand, because nothing in my own code had written down what actually happened. Not which host, not which of my two HTTP helper functions made the call, not a timestamp, nothing. The failure was real and the fix (get dev.to added to the environment's egress allowlist) was correct, but I found it by treating my own server as a black box and probing it from outside, which is exactly backwards for code I wrote myself. eight tools, one shared blind spot server.py is an 8-tool FastMCP server: three GitHub tools, four DEV.to tools, one that shells out to claude -p . Every HTTP-calling tool routes through one of two helpers: def _gh ( path , method = " GET " , data = None ): req = urllib . request . Request ( f " https://api.github.com { path } " , method = method ) req . add_header ( " Authorization " , f " token { os . environ [ ' GITHUB_TOKEN ' ] } " ) req . add_header ( " Accept " , " application/vnd.github.v3+json " ) if data : req . add_header ( " Content-Type " , " application/json " ) req . data = json . dumps ( data ). encode () with urllib . request . urlopen ( req ) as r : return json . loads ( r . read ()) def _dev ( path , method = " GET " , data = None ): req = urllib . request . Request ( f " https://dev.to/api { path } " , method = method ) req . add_header ( " api-key " , os . environ [ " DEV_TO_API " ]) req . add_header ( " Content-Type " , " application/json " ) req . add_header ( " User-Agent " , " developer-presence-mcp/1.0 " ) if data : req . data = json . dumps ( data ). encode () with urllib . request . urlopen ( req ) as r : return json . loads ( r . read ()) Neither one logs anything. When urlopen raises, the caller — whichever @mcp.tool() function invoked it — sees a bare urllib.error.HTTPEr